Dear Colleague,
First get the written complaint from the senior about the factual details of the incidence- date, time ,place and exact nature of misbehaviour.
Ascertain if the Employee has misbehaved for the first time as well as the seriousness of the misbehaviour. If it is minor and first time, just warn him in writing.
But if it is otherwise , issue him a show cause notice which also ensures giving him opportunity to explain before any punitive action is taken.
Depending upon his response, you may proceed further .
Please remember that the behavioural aberrations are two way process and sets into motion chain reaction. It will be crucial to decide who started it first and what were the provocations. It may not be the case that the Employee is always at fault, it could be the Senior also in which case it will be tight rope walk for the HR.
Regards,
Vinayak Nagarkar
HR and Employee Relations Consultant